The present invention relates to a microparticle sorting apparatus, a microchip and a microchip module. More particularly, the invention relates to a microparticle sorting apparatus for discharging a droplet containing therein a microparticle after having detected characteristics of the microparticle caused to flow through a flow path formed in a microchip, and controlling a movement direction of the droplet in accordance with the characteristics of the microparticle, thereby sorting the microparticles, a microchip and a microchip module.
Heretofore, there has been used an apparatus for introducing a dispersion liquid of microparticles to a flow path, thereby optically measuring characteristics of the microparticles thus introduced to the flow path in order to discriminate the characteristics of biologically-relevant microparticles such as a cell, a microbe, and a liposome, or microparticles such as synthetic particles, for example a latex particle, a gel particle, and an industrial particle.
In particular, with respect to the biologically-relevant microparticle, an apparatus called a flow cytometer is used in many cases. The flow cytometer, for example, is described in Non-Patent Document of “Additional Volume of Cell Engineering Experimental Protocol Series Flow Cytometry Capable of being Manipulated with Freedom,” by Hiromitsu Nakauchi Shujunsha Co., Ltd. second edition published on Aug. 31, 2006. Some flow cytometers are constructed so as to only aim at measuring the characteristics of the microparticles, and others are constructed so as to be capable of sorting only the microparticles each having the desired characteristics in accordance with the measurement results. Of the latter, in particular, the apparatus aimed at sorting the cells is called “a cell sorter.” At the present time, with the commercially-supplied cell sorter, the characteristics of the cells can be measured at a high speed of several thousands of cells per second to several tens of thousands of cells per second, thereby sorting the cells.
With the existing flow cytometer, the characteristics such as a size and a structure of a microparticle such as a cell or a microbead are measured in the following manner. Firstly, a sample liquid solution containing therein the microparticles each as an object of a measurement in a flow cell is caused to flow in the center of a laminar flow of a sheath liquid, thereby arranging the microparticles in line within the flow cell. Next, in an optically detecting portion, a measurement light is radiated to the microparticles arranged in line and caused to flow through the flow cell, and a scattered light or a fluorescence generated from the microparticle is detected, thereby measuring the characteristics of the microparticle. Subsequently, when the sorting for the microparticles is carried out, the sample solution is prepared as a droplet containing therein the microparticle, and the droplet is then discharged to a space in the outside of the flow cell. In this case, a movement direction of the droplet is controlled, thereby sorting the microparticles each having the desired characteristics.
Japanese Patent Application No. 2007-046947 (refer to FIG. 14) discloses an apparatus composed of a fluid system, an optical system, and a sorting system. In this case, with the fluid system, cells dyed with a fluorescence standard test solution or the like are arranged in line. With the optical system, a laser beam is radiated to the cell to detect the scattered light or the fluorescence generated from the cell. Also, with the sorting system, the movement direction of the droplet discharged to the space in the outside of the flow cell is controlled.
In those existing flow cytometers (cell sorters), the flow cell part or component composing the flow path system is made of expensive quartz. Also, each of those existing flow cytometers is composed of an orifice part or component separated from the flow cell. Thus, each of those existing flow cytometers does not have such a construction as to simply undergo disposable use for a user. For this reason, there is the possibility that even when the flow cell part or component, and the orifice part or component are sufficiently cleaned every time the measurement is carried out, cross-contamination of the samples are caused between the measurements. Such cross-contamination of the samples between the measurements, and the utilization of the expensive flow cell and orifice part or component become especially a large obstacle in such a case as to use the stem cells sorted by the cell sorter or the like in a regeneration medicine.
In recent years, a microchip in which an area and a flow path for carrying out an chemical and biological analysis are provided on a substrate made of silicon or a glass has been developed as the technique for solving the cross-contamination of the samples between the measurements, and the utilization of the expensive flow cell and orifice port or component. An analysis system using such a microchip is referred to as a Micro-Total-Analysis System (μ-TAS), a lab-on-chip, a biochip or the like.
A microparticle analysis technique for optically, electrically or magnetically analyzing the characteristics of the microparticle within the flow path or the area disposed on the microchip is known as an example of an application of the μ-TAS to the microparticle sorting technique. For example, Japanese Patent Application No. 2003-107099 discloses a microparticle sorting microchip having a flow path for guiding a liquid solution containing therein microparticles, a sheath flow forming path disposed at least on one side portion of the flow path, a microparticle measuring portion, and two or more microparticle sorting flow paths on a substrate. In this case, the microparticle measuring portion measures the microparticles introduced. Also, the two or more microparticle sorting flow paths are installed lower stream with respect to the microparticle measuring portion in order to sort and collect the microparticles. This microparticle sorting microchip has electrodes in the vicinity of a flow path hole from the microparticle measuring portion to the two or more microparticle sorting flow paths. According to a microparticle sorting apparatus including this microparticle sorting microchip, the movement direction of the microparticles can be controlled in accordance with an interaction with an electric field generated between the electrodes, thereby sorting the microparticles.
With a flow cytometer (cell sorter) to which the μ-TAS is applied, the flow path system can be composed of the microchip which can undergo the dispensable use. Therefore, no cross-contamination of the samples is generated between the measurements. In addition, since the sorting system can be constructed within an air-tight flow path disposed on the chip, the sample is prevented from being commingled with a pollutant such as an aerosol during the measurement. On the other hand, however, the liquid containing therein the microparticles needs to be fed at a high pressure to the flow path disposed on the chip, and thus the control for the movement direction of the microparticles need to be carried out in a state in which the microparticles are caused to flow within the liquid. For this reason, it is difficult to increase the flowing speed and the sorting speed of the microparticles, and thus it is difficult to measure the characteristics of the cells at the high speed of the several thousands of the cells per second to several tens of thousands of the cells per second, thereby sorting the cells like in the manner of the existing flow cytometer (cell sorter).